Position information acquisition device, position information acquisition method, recording medium, and position information acquisition system

ABSTRACT

A position information acquisition device for acquiring position information of a position acquisition target arranged in a space includes a processor configured to detect light that is based on identification information included in-common in captured images that are images of the space captured from a plurality of shooting directions that are different from each other, acquire a three-dimensional position in the space of the position information acquisition target identified by the identification information, based on detection positions of the detected light in the captured images, and position information of image capturing devices during capturing performed by the image capturing devices, acquire reliability degree information of the acquired three-dimensional position of the position information acquisition target, based on information relating to an imaging state of each image capturing device during capturing of the captured images, and store the acquired the reliability degree information in a storage.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Japanese Patent Application No.2018-224457, filed on Nov. 30, 2018, and Japanese Patent Application No.2019-105599, filed on Jun. 5, 2019, of which the entirety of thedisclosures is incorporated by reference herein.

FIELD

The present disclosure relates to a position information acquisitiondevice, a position information acquisition method, a recording medium,and a position information acquisition system.

BACKGROUND

As described in International Publication No. WO2005/124687, technologyis known heretofore that identifies three-dimensional positions ofmultiple markers by using multiple cameras to image markers.

SUMMARY

According to the present disclosure, a position information acquisitiondevice for acquiring position information of a position acquisitiontarget arranged in a space includes a processor configured to

detect light that is based on identification information includedin-common in captured images that are images of the space captured froma plurality of shooting directions that are different from each other,

acquire a three-dimensional position in the space of the positioninformation acquisition target identified by the identificationinformation, based on detection positions of the detected light in thecaptured images, and position information of image capturing devicesduring capturing performed by the image capturing devices by which theimages are captured,

acquire reliability degree information of the acquired three-dimensionalposition of the position information acquisition target, based oninformation relating to an imaging state of each image capturing deviceof the image capturing devices during capturing of the captured images,and

store the acquired the reliability degree information in a storage.

In the present disclosure, a position information acquisition method foracquiring position information of a position acquisition target arrangedin a space includes:

detecting light that is based on identification information includedin-common in captured images that are images of the space captured froma plurality of shooting directions that are different from each other;

acquiring a three-dimensional position in the space of the positioninformation acquisition target identified by the identificationinformation, based on detection positions of the detected light in thecaptured images, and position information of image capturing devicesduring capturing performed by the image capturing devices by which theimages are captured;

acquiring reliability degree information of the acquiredthree-dimensional position of the position information acquisitiontarget, based on information relating to an imaging state of each imagecapturing device of the image capturing devices during capturing of thecaptured images; and

storing the acquired the reliability degree information in a storage.

In the present disclosure, a non-transitory computer-readable recordingmedium records a program that causes a computer included in a positioninformation acquisition device for acquiring position information of aposition acquisition target arranged in a space to function as:

detection means for detecting light that is based on identificationinformation included in-common in captured images that are images of thespace captured from a plurality of shooting directions that aredifferent from each other;

means for acquiring a three-dimensional position in the space of theposition information acquisition target identified by the identificationinformation, based on detection positions of the detected light in thecaptured images, and position information of image capturing devicesduring capturing performed by the image capturing devices by which theimages are captured,

means for acquiring reliability degree information of the acquiredthree-dimensional position of the position information acquisitiontarget, based on information relating to an imaging state of each imagecapturing device of the image capturing devices during capturing of thecaptured images, and

means for storing the acquired the reliability degree information in astorage.

In the present disclosure, a position information acquisition systemincludes:

image capturing devices configured to capture images of a space from aplurality of shooting directions that are different from each other; and

a position information acquisition device configured to acquire positioninformation of a position acquisition target arranged in the space.

The position information acquisition device includes a processorconfigured to

detect light that is based on identification information includedin-common in captured images that are images captured by the imagecapturing devices,

acquire a three-dimensional position in the space of the positioninformation acquisition target identified by the identificationinformation, based on detection positions of the detected light in thecaptured images, and position information of the image capturing devicesduring capturing performed by image capturing devices by which theimages are captured,

acquire reliability degree information of the acquired three-dimensionalposition of the position information acquisition target, based oninformation relating to an imaging state of each image capturing deviceof the image capturing devices during capturing of the captured images,and

store the acquired the reliability degree information in a storage.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of this application can be obtained whenthe following detailed description is considered in conjunction with thefollowing drawings, in which:

FIG. 1 illustrates an example of a visible light communication systemaccording to an embodiment of the present disclosure;

FIG. 2 illustrates an example of configuration of a server according tothe same embodiment;

FIG. 3 illustrates an example of parallax obtained from images capturedby two cameras according to the same embodiment;

FIG. 4 illustrates an example of calculation of arrangement positionsand imaging directions of two cameras according to the same embodiment;

FIG. 5 illustrates an example of velocity calculation according to thesame embodiment;

FIG. 6 illustrates an example of spatial partitioning according to thesame embodiment;

FIG. 7 is a flowchart illustrating an example of reliability degreeinformation acquisition by the server according to the same embodiment;

FIG. 8 is a flowchart illustrating an example of acquisition processingof an arrangement position of a second marker by the server according tothe same embodiment;

FIG. 9 is a flowchart illustrating an example of generating andretaining a position-reliability degree information table by a serveraccording to another embodiment;

FIG. 10 illustrates an example of the position-reliability degreeinformation table according to the other embodiment;

FIG. 11 is a flowchart illustrating an example of generating andretaining a position-reliability degree information table by the serveraccording to the other embodiment;

FIG. 12 illustrates an example of the position-reliability degreeinformation table according to the other embodiment; and

FIG. 13 illustrates an example of positional error calculation accordingto the other embodiment.

DETAILED DESCRIPTION

A visible light communication system is described below as a positioninformation acquisition system according to an embodiment of the presentdisclosure with reference to drawings.

FIG. 1 illustrates configuration of the visible light communicationsystem. As illustrated in FIG. 1, the visible light communication system1 is configured to include: apparatuses 100 a, 100 b, and 100 cabbreviated below appropriately as the “apparatus 100” when not limitedto a given apparatus 100 a, 100 b, or 100 c) arranged within a space500; and a server 200 corresponding to a position informationacquisition device.

A second marker 102 a is attached to the apparatus 100 a; a secondmarker 102 b is attached to the apparatus 100 b; a second marker 102 cis attached to the apparatus 100 c; and these markers are abbreviatedbelow appropriately as the “second marker 102” when not limited to agiven second marker 102 a, 102 b, or 102 c. Cameras 201 a, 201 b, 201 c,and 201 d corresponding to image capturing devices are attached to theserver 200; and are abbreviated below appropriately as the “camera 201”when not limited to a given camera 201 a, 201 b, 201 c, or 201 d.Moreover, first markers 300 a, 300 b, 300 c, 300 d, and 300 e arearranged within the space 500; and are abbreviated below appropriatelyas the “first marker 300” when not limited to a given first marker 300a, 300 b, 300 c, 300 d, or 300 e. The first marker 300 and the secondmarker 102 each include a non-illustrated light emitting diode (LED).The second marker 102 corresponds to a position information acquisitiontarget.

In the present embodiment, the second marker 102 attached to theapparatus 100 transmits information by emitting light corresponding toinformation of various types of transmission targets such as a state ofthe apparatus 100. The server 200 demodulates changes in emitted-lightcolor in images of light obtained by time-series type capturing by thecameras 201, and acquires information emitted by the second marker 102.

In the present embodiment, positions and imaging directions of thecameras 201 a to 201 d are initially unknown. Thus prior to theacquiring by the server 200 of information such as the state of theapparatus 100, firstly the positions (arrangement positions) and theimaging directions of the cameras 201 a to 201 d in the space 500 thatis a three-dimensional space are calculated by the server 200 on thebasis of the positions, as two-dimensional coordinate information, ofeach representation of the first markers 300 a, 300 b, 300 c, 300 d, and300 e in the images captured by the cameras 201 a to 201 d. The server200 generates a conversion matrix for converting positions(two-dimensional coordinate information) of the images of the firstmarkers 300 in the images obtained by capturing into positions(arrangement positions) within the space 500.

FIG. 2 illustrates an example of configuration of the server 200. Asillustrated in FIG. 2, the server 200 includes a controller 202, animage input unit 204, a storage 205, an operation device 206, a display207, and a communication device 208. The server 200 is attached throughlines to the cameras 201 a to 201 d.

The camera 201 a includes a lens 203 a; the camera 201 b includes a lens203 b; the camera 201 c includes a lens 203 c; the camera 201 d includesa lens 203 d; and the lenses are abbreviated below appropriately as the“lens 203” when not limited to a given lens 203 a, 203 b, 203 c, or 203d. The lens 203 includes components such as a zoom lens. The lens 203moves due to a zoom control operation from the operation device 206 andfocal control by the controller 202. The view angle and/or optical imagecaptured by the camera 201 is controlled by movement of the lens 203.

The cameras 201 a to 201 d each include multiple light-receivingelements orderly disposed in a two-dimensional array on alight-receiving surface. The light-receiving element is an imagecapturing device such as a charge coupled device (CCD), a complementarymetal oxide semiconductor (CMOS), or the like. Each of the cameras 201 ato 201 d captures an optical image from light entering through the lens203 (receives light) in the view angle of a prescribed range on thebasis of a control signal from the controller 202, and generates a frameby converting the image signal within the imaged view angle to digitaldata. Further, each of the cameras 201 a to 201 d continues over timewith the imaging and the frame generation, and outputs the continuingframe to the image input unit 204 within the server 200.

On the basis of the control signal from the controller 202, the frame(digital data) output from the camera 201 is input to the image inputunit 204.

The controller 202 is a processor that includes components such as acentral processing unit (CPU). The controller 202 controls various typesof functions with which the server 200 is equipped by executing softwareprocessing in accordance with programs, that is, programs for achievingoperations of the server 200 illustrated in a below-described FIG. 3,stored in the storage 205.

The storage 205 is random access memory (RAM) and/or read only memory(ROM), for example. The storage 205 stores various types of information,such as programs, used in operations such as control by the server 200.

The operation device 206 includes components such as a numeric keypadand/or function keys, and is an interface that is used for input ofoperational content of a user. The display 207 includes a display suchas a liquid crystal display (LCD), a plasma display panel (PDP), anelectro-luminescence (EL) display, or the like. The display 207 displaysan image in accordance with an image signal output from the controller202. The communication device 208 is a device such as a local areanetwork (LAN) card. Under control by a communication controller 242, thecommunication device 208 performs communication with an externalcommunication device.

The controller 202 includes an image processor 231, a cameraposition-imaging direction calculator 232, a matrix generator 234, alight-emission position acquirer 236 corresponding to calculation means,an imaging state acquirer 238 corresponding to information acquisitionmeans, a reliability degree information acquirer 240 corresponding toreliability degree information acquisition means, and the communicationcontroller 242.

The image processor 231 adjusts image quality and/or image size byperforming peripheral darkening correction and/or distortion correctionto allow display of, as a through image on the display 207, a frame,that is, digital data, output from each of the cameras 201 and input tothe image input unit 204. The image processor 231 has functions for,upon input of a control signal based on the command operation from theoperation device 206, encoding and file generation from the opticalimage within the view angle of the camera 201 or the optical image inthe display range displayed on the display 207 at the time of thecommand, the encoding and file generation using a compression-encodingformat such as the joint photographic experts group (JPEG) format. Thecamera position-imaging direction calculator 232 calculates the position(two-dimensional coordinate information) of representations of the firstmarker 300 in each of the images captured by the cameras 201 a to 201 d.Here, the arrangement positions (three-dimensional coordinateinformation) of the first markers 300 a, 300 b, 300 c, 300 d, and 300 ewithin the space 500 are assumed to be previously known. Each of thefirst markers 300 a, 300 b, 300 c, 300 d, and 300 e emits light thatchanges cyclically in a pattern of three colors red (R), green (G), andblue (B) modulated with an identification (ID) that enables uniqueidentification of the marker.

The camera position-imaging direction calculator 232, from among thecameras 201 a to 201 d, sets combinations of cameras as pairs of cameras201, that is, camera pairs. Six patterns (six sets) result from makingcombinations of pairs of the cameras 201 freely from among 4 cameras201.

The camera position-imaging direction calculator 232 detects light ofthe cyclical three-colored patterns included in various images capturedby the cameras 201 a to 201 d. Further, the camera position-imagingdirection calculator 232 attempts detecting the ID corresponding to thepattern of light emitted in these three colors, and attemptsdemodulating into the ID. The storage 205 stores the arrangementposition in association with the ID for each of the first marker 300 a,300 b, 300 c, 300 d, and 300 e.

Further, the camera position-imaging direction calculator 232, for eachcamera pair, attempts detection of modulation light regions (pixelregions formed from an identified size and shape and having a luminosityvalue of at least a predetermined value) in which light is modulatedwith the same ID, from among both images captured by the pair of cameras201 included in the camera pair. Thereafter, if the detection succeeds,the first marker 300 corresponding to the ID thereof is regarded to bedetectable. For each camera pair, the camera position-imaging directioncalculator 232 further recognizes a detection count of the first markers300.

Thereafter, for each of the camera pairs, the camera position-imagingdirection calculator 232 sets an algorithm for calculation of theposition (arrangement position) and imaging direction in the space 500of the two cameras 201 included in the camera pair, in accordance withthe count of the first markers 300 included in both of the imagescaptured by the pair of cameras 201 included in the camera pair. Thecount of prepared algorithms depends on the count of first markers 300included in the images, such as, for example, preparation of 5algorithms in the case in which the count of the first markers 300included in the images captured by the camera pair is 5, and preparationof 8 algorithms in the case in which the count is 8, and the preparedalgorithms are stored in the storage 205.

Thereafter, for each of the camera pairs, the camera position-imagingdirection calculator 232 uses the set algorithm to calculate thearrangement positions and the imaging directions of the two cameras 201included in the camera pair.

The algorithm is described below. FIG. 3 illustrates an example ofparallax obtained from images captured by the cameras 201. Moreover,FIG. 4 illustrates an example of calculation of the arrangementpositions and the imaging directions of the camera 201.

As illustrated in FIG. 3, in the case of capture of the same firstmarker 300 c by two cameras 201 (in this case, cameras 201 a and 201 b)included in the camera pair, the arrangement positions of the camera 201a and the camera 201 b are different from each other, and thus parallaxS occurs between a position (two-dimensional coordinate information) ofa representation 251 a of the first marker 300 c in the image of animaging plane 250 a captured by the camera 201 a and a position(two-dimensional coordinate information) of a representation 251 b ofthe first marker 300 c in the image of an imaging plane 250 b capturedby the camera 201 b.

Moreover, a distance calculation formula D=B×F/S is established inwhich, as illustrated in FIG. 4, F (same value) is taken to be adistance to the focal position from the imaging plane 250 a of one ofthe cameras 201 (camera 201 a in this case) among the two cameras 201(cameras 201 a and 201 b in this case) included in the camera pair, F(same value) is taken to be a distance to the focal position from theimaging plane 250 b of the other camera 201 (camera 201 b in this case),B is taken to be a distance between the arrangement positions of thecamera 201 a and the camera 201 b, D is taken to be a shortest distancebetween the first marker 300 c and a straight line interconnecting thefocal position of the camera 201 a and the focal position of the camera201 b, and S is taken to be the parallax between the position of therepresentation 251 a and the position of the representation 251 b of thefirst marker 300 c obtained by virtual overlapping of the imaging plane250 a and the imaging plane 250 b. In this formula, F and S are taken tobe previously known constants.

In the present embodiment, the camera position-imaging directioncalculator 232 sets up the respective distance calculation formula foreach of the detected first markers 300, rather than just setting up thedistance calculation formula for the first marker 300 c. Further, thecamera position-imaging direction calculator 232 calculates thearrangement positions and the captures directions of the two cameras 201included in the camera pair, on the basis of the set distancecalculation formula and the arrangement positions of the first markers300 measured beforehand.

Specifically, the camera position-imaging direction calculator 232determines the relative arrangement positions and the imaging directionsof the two cameras 201 from a combination of positions (Xga1, Yga1) ofthe representation 251 a of the first marker 300 included in the imagecaptured by one of the cameras 201 of the two cameras 201 included inthe camera pair and positions (Xgb1, Ygb1) of the representation 251 bof the first marker 300 included in the image captured by the othercamera 201.

Next, the camera position-imaging direction calculator 232 refers to theIDs of the first markers 300 a to 300 e to read the arrangementpositions of the first markers 300 a to 300 e stored in the storage 205,and uses such read arrangement positions to calculate the arrangementpositions and the imaging directions in the space 500 of the two cameras201 included in the camera pair. Then the matrix generator 234determines a conversion matrix capable of conversion to the arrangementposition (position information defined in three-dimensional spacecoordinates) of the first marker 300 in the space 500, from thecombination of the position (two-dimensional coordinate information) ofthe representation of the first marker 300 included in the imagecaptured by one of the cameras 201 and the position (two dimensionalcoordinate information) of the representation of the first marker 300included in the image capture by the other of the cameras 201, based onthe calculated arrangement positions and the imaging directions of theone camera 201 and the other camera 201. The conversion matrix isdetermined for each pair of cameras.

The second markers 102 a, 102 b, and 102 c emit light that changescyclically in a three-color pattern of red (R), green (G), and blue (B)modulated with the ID that enables unique identification of the marker.

After the determination of the conversion matrixes for each of thecamera pairs, the light-emission position acquirer 236 detects light ofthe cyclical pattern of three colors included in the various imagescaptured by the cameras 201 a to 201 d. Further, the light-emissionposition acquirer 236 attempts detection of the IDs, and demodulation tothe IDs, corresponding to the patterns of such three-coloredlight-emission. In the case in which detecting the same ID from both ofthe images captured by the two cameras 201 included in the camera pairis possible, the light-emission position acquirer 236 regards the secondmarker 102 corresponding to such an ID to be detectable.

Thereafter, for each of the camera pairs, the light-emission positionacquirer 236 acquires a position (Xga2, Yga2) of a representation of thesecond marker 102 in the imaging plane of one of the cameras 201 amongthe two cameras 201 included in the camera pair and a position (Xgb2,Ygb2) of a representation the second marker 102 in the imaging plane ofthe other cameras 201. Further, the light-emission position acquirer 236acquires the combination of the positions (Xga2, Yga2) and (Xgb2, Ygb2)of both representations, and uses the conversion matrix to acquire thearrangement position (Xk2, Yk2, Zk2) of the second marker 102 in thespace 500.

The aforementioned processing is a case in which arrangement positionscorresponding to each of multiple camera pairs are acquired by use of asingle second marker 102. In such a case, reliability degreeinformation, that is, likelihood information, of the arrangementposition within the space 500 is acquired for the second marker 102 foreach of the camera pairs. The acquiring of the reliability degreeinformation is described below.

For each camera pair, the imaging state acquirer 238 sets thereliability degree relating to the position of the representation of thesecond marker 102 in the acquired image from the imaging plane of onecamera 201 among the two cameras 201 included in this camera pair suchthat the reliability degree is set higher as the position of therepresentation approaches the center of the image, and is set lower withincreased distance of the position of the representation from thecenter. In the same manner, the imaging state acquirer 238 set thereliability degree relating to the position of the representation of thesecond marker 102 in the acquired image from the imaging plane of theother camera 201 such that the reliability degree is set higher as theposition of the representation approaches the center of the image, andis set lower with increased distance of the position of therepresentation from the center. Such setting processing is related todistortion correction processing in the image processor 231; thisdistortion correction processing lessens correction intensity ofdistortion correction with increased closeness to the center in theimaging plane; and this distortion correction processing increases thecorrection intensity of distortion correction with increased closenessto the periphery. Therefore, as the position of the representation ofthe second marker 102 approaches the periphery, positional displacementdue to distortion correction occurs that decreases the reliabilitydegree.

Due to the aforementioned processing, reliability degree information(image position reliability degree information) B1 is acquired relatingto the image position with respect to one second marker 102 underconsideration for one of the cameras 201 among the two cameras 201included in the camera pair, and reliability degree information (imageposition reliability degree information) B2 is acquired relating to theimage position with respect the one second marker 102 underconsideration for the other camera 102 among the two cameras 201included in the camera pair.

Moreover, the imaging state acquirer 238 refers to multiple frames(images) acquired by consecutive capture by one of the cameras 201 amongthe two cameras 201 included in the camera pair, and calculates movementvelocity of the second marker 102 on the basis of change of the positionof the second marker 102.

FIG. 5 illustrates an example of the velocity calculation. For example,the position of the representation of the second marker 102 in a frameF1 among multiple frames F1, F2, . . . Fn captured consecutively along atime direction t is “710 a”, and the position of the representation ofthe second marker 102 in the frame Fn is “710 n”. A case is consideredbelow in which L is a distance between the positions 710 a and 710 n ofthe representation in a frame Fx that superimposes the frames F1 and Fnon each other. In such a case, as a result of a comparison between sizesof the representation of the second marker 102 in both frames versus asize of the second marker 102 that is previously known and storedbeforehand in the storage 205, the imaging state acquirer 238 cancalculate the movement velocity of the second marker 102 on the basis ofthe distance L and a frame rate. Further, the imaging state acquirer 238sets the reliability degree of such movement velocity higher withincreased slowness of the movement velocity, that is, with decreaseddistance L.

Similarly, the imaging state acquirer 238 calculates the movementvelocity of this second marker 102 from the distance L between thepositions of the representations of the second marker 102 in the imagescaptured consecutively by the camera 201 that is the other camera 201among the two cameras 201 included in the camera pair. Further, withrespect to the reliability degree relating to such movement velocity,the imaging state acquirer 238 sets the velocity reliability degreehigher with increased slowness of the movement velocity, that is, withdecrease in the distance L.

The aforementioned processing is executed due to the possibility thatthe arrangement position changes, even when the second marker 102 isfixed at the same arrangement position for a long period, since the viewangle of the camera 201 may change slightly and/or the second marker 102may move slightly. Specifically, reliability degree information(velocity reliability degree information) C1 relating to the movementvelocity with respect to the second marker 102 is acquired concerningone of the cameras 201 among the two cameras 201 included in the camerapair, and reliability degree information (velocity reliability degreeinformation) C2 relating to the movement velocity with respect to thesame second marker 102 is acquired concerning other camera 201.

Moreover, the imaging state acquirer 238 partitions the space 500 intomultiple regions. FIG. 6 is an example of the spatial partitioning. InFIG. 6, 9 regions, that is, partitioning regions, 501 a, 501 b, 501 c,501 d, 501 e, 501 f, 501 g, 501 h, and 501 i (abbreviated belowappropriately as the “partitioning region 501” when not limited to agiven partitioning region 501 a to 501 i) are formed by dividing theimage longitudinally into three equally dimensioned portions anddividing the image laterally into three equally dimensioned portions.

Further, on the basis of the relative positional relationship betweenthe arrangement position of one of the second markers 102 underconsideration and the arrangement positions of the two cameras 201included in the camera pair, the imaging state acquirer 238 acquiresreliability degree information D, that is, arrangement positionreliability degree information, relating to the arrangement position ofthis second marker 102.

Specifically, due to the ability to capture a larger representation ofthe second marker 102, the imaging state acquirer 238 sets thearrangement position reliability degree higher with increased closenessto the arrangement position of the two cameras 201 included in thecamera pair. For example, in the case in which the camera 201 a and thecamera 201 d are arranged as illustrated in FIG. 6, the arrangementposition degree is set a high value when the second marker 102 ispresent in the partitioning region 501 a, 501 b, or 501 c; thearrangement position reliability degree is set to an intermediate valuewhen the second marker 102 is present in the partitioning region 501 d,501 e, or 501 f; and the arrangement position reliability degree is setlow when the second marker 102 is present in the partitioning region 501g, 501 h, or 501 i.

Moreover, for each pair of cameras, the reliability degree informationacquirer 240 calculates an arrangement position, that is, positioninformation defined by three-dimensional space coordinates, of the firstmarker 300 within the space 500, for the representations of the firstmarker 300 captured by both of the cameras 201 included the camera pair,by using the conversion matrix corresponding to the camera pair incombination with the position (two-dimensional coordinate information)captured by one of the cameras 201 and the position (two-dimensionalcoordinate information) captured by the other camera 201. Further, thereliability degree information acquirer 240 calculates an error betweenthe calculated arrangement position of the first marker 300 within thespace 500 and the arrangement position (previously known information) ofthe first marker 300 stored in the storage 205. Further, the reliabilitydegree information acquirer 240 sets an error reliability degreeinformation A so as to increase in reliability degree (error reliabilitydegree) concerning the error with decrease in the error.

Thereafter, for each camera pair, the reliability degree informationacquirer 240 calculates reliability degree information (reliabilitydegree information of the second marker 102) N concerning thearrangement position calculation for one second marker 102 underconsideration by use of the image position reliability degreeinformation B1 and B2, the velocity reliability degree information C1and C2, the arrangement position reliability degree information D, andthe error reliability degree information A acquired in theaforementioned processing. For example, the calculation is by a formulaN=A×(B1+B2+C1+C2+D).

Thereafter, the light-emission position acquirer 236 calculates thearrangement position of the second marker 102 within the space 500.During this calculation, sometimes the arrangement positions frommultiple pairs of cameras are calculable for one second marker 102 underconsideration. In such a case, for the one second marker 102 underconsideration, the light-emission position acquirer 236 compares thereliability degree information N acquired for each camera pair. Then thelight-emission position acquirer 236 selects the camera paircorresponding to the reliability degree information N that is highest.

Thereafter, the light-emission position acquirer 236 acquires theposition (two-dimensional coordinate information) of the representationof the second marker 102 in the image captured by one camera 201 amongthe selected camera pair and the position (two-dimensional coordinateinformation) of the representation of the second marker 102 in the imagecaptured by the other camera 201. Further, the light-emission positionacquirer 236 uses the conversion matrix and the combination of thepositions of these two representations to calculate the arrangementposition (position information defined by three-dimensional spacecoordinates) of the second marker 102 within the space 500.

Operation of the server 200 is described below with reference toflowcharts. FIG. 7 is a flowchart illustrating an example of reliabilitydegree information acquisition by the server 200. The operationillustrated in FIG. 7 is performed for each camera pair, and for eachfirst marker 300 captured by both of two cameras included in the camerapair.

The two cameras 201 included in the one camera pair capture the samefirst marker 300, and the first marker 300 is identified on the basis ofthe acquired ID (step S101).

Next, the imaging state acquirer 238 acquires the image position degreereliability information B1 such that the image position reliabilitydegree increases, for the position of the representation of the secondmarker 102 in the image captured by one of the cameras 201 among the twocameras 201 included in the camera pair, with increased closeness to thecenter of the captured image, and acquires the image position degreereliability information B2 such that the image position reliabilitydegree increases, for the position of the representation of the secondmarker 102 in the image captured by the other camera 201, with increasedcloseness to the center of the captured image (step S102).

Thereafter, on the basis of each of the images captured consecutively byone of the cameras 201 among the two cameras 201 included in the camerapair, the imaging state acquirer 238 calculates the movement velocity ofthe second marker 102, and acquires the velocity reliability degreeinformation C1 such that the velocity reliability degree increases withincreased slowness of the movement velocity. In a similar manner, on thebasis of each of the images captured consecutively by the other camera201, the imaging state acquirer 238 calculates the movement velocity ofthe second marker 102, and acquires the velocity reliability degreeinformation C1 such that the velocity reliability degree increases withincreased slowness of the movement velocity (step S103).

Thereafter, on the basis of the positional relationship between thearrangement position of the two cameras 201 included in the camera pairand the arrangement position of the second marker 102, the imaging stateacquirer 238 acquires the arrangement position reliability degreeinformation D such that the arrangement position reliability degreeincreases with increased closeness of the arrangement position of thesecond marker 102 to the arrangement position of the two cameras 201included in the camera pair (step S104).

Thereafter, concerning the representation of the first marker 300captured by both of the two cameras 201 included in the camera pair, thereliability degree information acquirer 240 uses the conversion matrixcorresponding to the camera pair and the combination of the positionobtained by capture by one of the cameras 201 and the position obtainedby capture by the other camera 201 to calculate the arrangement positionof the first marker 300 within the space 500. The reliability degreeinformation acquirer 240 calculates the error between the calculatedarrangement position of the first marker 300 within the space 500 andthe arrangement position (previously known information) of the firstmarker 300 stored in the storage 205, and acquires the error reliabilitydegree information A such that the error reliability degree increaseswith increased smallness of the error (step S105).

Further, the reliability degree information acquirer 240 acquires thereliability degree information N of the second marker 102 by using theacquired image position reliability degree information B1 and B2, thevelocity reliability degree information C1 and C2, the arrangementposition reliability degree information D, and the error reliabilitydegree information A (step S106).

FIG. 8 is a flowchart illustrating an example of acquisition processingof the arrangement position of the second marker 102 by the server 200.Multiple cameras 201 capture the second marker 102 within the space 500(step S201).

Thereafter, for a single second marker 102, in the case in whichmultiple camera pairs exist in which both of the two cameras 201 capturethe second marker 102, the light-emission position acquirer 236 selectsthe reliability degree information that is highest among the reliabilitydegree information of the second marker 102 acquired by each of thesemultiple camera pairs. Further, the light-emission position acquirer 236selects the camera pair that corresponds to such selected reliabilitydegree information (step S202).

Thereafter, the light-emission position acquirer 236 acquires theposition of the representation of the second marker 102 in the imagecaptured by one camera 201 among the selected camera pair and theposition of the representation of the second marker 102 in the imageacquired captured by the other camera 201. Further, the light-emissionposition acquirer 236 uses the conversion matrix and the combination ofthe two acquired positions to calculate the arrangement position of thesecond marker 102 (step S203).

Thereafter, the light-emission position acquirer 236 determines whetherthe arrangement position is calculated for all the second markers 102captured in step S201 (step S204). If the arrangement positions arecalculated for all of the second markers 102 (YES in step S204), thesequence of processing ends. Moreover, if a second marker 102 exists forwhich the arrangement position is not calculated (NO in step S204), theoperations of step S202 and beyond are repeated.

In the present embodiment in this manner, for each of the camera pairs,the server 200 acquires the reliability degree information concerningthe calculation of the arrangement position the second marker from thepositions of the second marker 102 in the images captured by both of thetwo cameras 201 included in the camera pair. Further, the server 200calculates the arrangement position of the second marker 102 on thebasis of the images captured by the camera pair. At this time, in thecase in which the arrangement position of the second marker 102 iscalculable for each of the camera pairs by capturing the second marker102 by multiple camera pairs, the server 200 selects the camera pairhaving the highest reliability degree of the second marker 102, andcalculates the arrangement position of the second marker 102 on thebasis of the images captured by such a pair of cameras. Due to suchoperation, the arrangement position of the second marker 102 iscalculable on the basis of the camera pair having a high reliabilitydegree of the second marker 102, and accuracy of the calculation can beimproved.

Specifically, the server 200 acquires the image position reliabilitydegree information such that the image position reliability degree ofthe image position of the second marker 102 in the captured imageincreases as the image position of the second marker 102 approaches thecenter of the image. Due to such operation, the reliability degree ofthe second marker 102 can decrease with increased distance of the imageposition of the second marker 102 from the center of the image, andreliability degree information can be acquired that is suitable inaccordance with the characteristic of the image that is increaseddistortion with increased separation from the center.

Moreover, the server 200 calculates the velocity of the second marker102 on the basis of the captured images, and acquires the velocityreliability degree information such that the velocity reliability degreeincreases with increased slowness of the velocity. Due to suchoperation, reliability degree information can be acquired that issuitable in accordance with the lowering of calculation accuracy of thearrangement position of the second marker 102 with increase in themovement velocity.

Moreover, the server 200 acquires the arrangement position reliabilitydegree information such that the arrangement position reliability degreeis higher with increased closeness of the arrangement position of thesecond marker 102 to the arrangement positions of the two cameras 201included in the camera pair. Due to such operation, reliability degreeinformation can be acquired that is suitable in accordance with thedecrease in calculation accuracy of the arrangement position withincreased distance of separation from the cameras 201 in generaltriangulation.

Moreover, the server 200 calculates the error between the calculatedarrangement position of the first marker 300 within the space 500 andthe previously known information of the arrangement position of thefirst marker 300, and acquires the error reliability degree informationsuch that the error reliability degree increases with increasedsmallness of this error. Due to such operation, the camera pair having asmall error, that is, having high calculation accuracy, can beprioritized for use in the calculation of the arrangement position ofthe second marker 102.

Another embodiment is explained below. In the present embodiment, thevisible light communication system 1 is similar to that of FIG. 1, andthe server 200 is similar to that FIG. 2. In the present embodiment,arrangement positions of the first marker 300 and the second marker 102are multiply calculated with respect to one marker, and reliabilitydegree information is set with respect the respective arrangementpositions.

FIG. 9 is a flowchart illustrating an example of generating andretaining the position-reliability degree information table by theserver 200 according to the other embodiment. The operations illustratedin FIG. 9 are performed for each of the first markers 300.

For each of the camera pairs, upon capture of the same first marker 300by the two cameras 201 included in the camera pair, this captured imageis acquired via the image input unit 204, and the controller 202attempts to identify the first marker 300 by controller ID acquisition(step S301).

Thereafter, the camera position-imaging direction calculator 232 in stepS301 captures the first marker, and selects a camera pair capable ofacquiring the ID (step S302).

Thereafter, for each camera pair selected in step S302, thelight-emission position acquirer 236 calculates the arrangement positionof the first marker 300 on the basis of the captured image captured bythe two cameras 201 included in the camera pair (step S303).Specifically, similarly to step S203 in FIG. 8, the light-emissionposition acquirer 236 acquires the position of the representation of thefirst marker 300 in the image captured by one of the cameras 201 amongthe camera pair and the position of representation of the first marker300 in the image captured by the other camera 201. Further, thelight-emission position acquirer 236 calculates the arrangement positionof the first marker 300 by using the conversion matrix corresponding tothe camera pair and the combination of such two acquired positions.

Next, the reliability degree information acquirer 240 generates, andretains in the storage 205, a position-reliability degree informationtable 2051 concerning the first marker 300 for which the arrangementposition is calculated in step S303 (step S304).

FIG. 10 illustrates an example of the generated position-reliabilitydegree information table 2051 retained in a certain storage region ofthe storage 205 in step S304. The position-reliability degreeinformation table 2051 illustrated in FIG. 10 includes, for each firstmarker 300 that is a marker: the ID of the first marker 300, thearrangement positions captured by the camera pairs capturing the firstmarker 300, the information of the camera pair capturing the image usedin the calculation of the arrangement position, the reliability degreeinformation of the arrangement position, the update time and dateindicating the time and date of calculation of the arrangement position,and the error.

The reliability degree information is set in three stages as A, B, and Cin order of decreasing reliability degree. For the first marker 300, thereliability degree information acquirer 240 sets the reliability degreeinformation by suitably selecting the image position reliability degreeinformation acquired in a manner similar to that of step S102 in FIG. 7,the velocity reliability degree information acquired in a manner similarto that of step S103 in the same drawing, the arrangement positionreliability degree information acquired in a manner similar to that ofstep S104 in the same drawing, and the error reliability degreeinformation acquired in a manner similar to that of step S105 in thesame drawing, or the like.

The error is set in three stages as R1, R2, and R3 in order ofincreasing size of the error. The reliability degree informationacquirer 240, for example, sets the error so as to be smaller withincreased approach of the update time and date to the present time anddate.

FIG. 11 is a flowchart illustrating another example of generating andretaining the position-reliability degree information table by theserver 200 according to another embodiment. The operation illustrated inFIG. 11 is performed for each second marker 102.

For each camera pair, the two cameras 201 included in the camera paircapture the same second marker 102, and by acquiring the ID, attempt toidentify the second marker 102 by ID acquisition (step S401).

The camera position-imaging direction calculator 232 selects the camerapairs capable of capturing the second marker 102 and acquiring the ID instep S401 (step S402).

Next, for each of the camera pairs selected in step S402, thelight-emission position acquirer 236 calculates the arrangement positionof the second marker 102 on the basis of the captured image captured bythe pair of cameras 201 included in the camera pairs (step S403).Specifically, in a manner similar to that of step S203 in FIG. 8, thelight-emission position acquirer 236 acquires the representation of thesecond marker 102 in the image captured by one of the cameras 201 amongthe camera pair, and acquires the position of the representation of thesecond marker 102 in the image captured by the other camera 201.Further, the light-emission position acquirer 236 calculates thearrangement position of the second marker 102 by using the conversionmatrix corresponding to the camera pair and the combination of these twoimage positions.

Thereafter, the reliability degree information acquirer 240 generatesposition-reliability degree information concerning the second marker 102for which the arrangement position is calculated in step 403, andappends and retains such position-reliability degree information in theposition-reliability degree information table 2051 (step S404).

FIG. 12 illustrates an example of a position-reliability degreeinformation table 2052 in step S404. FIG. 12 illustrates theposition-reliability degree information table 2052 obtained by appendingthe position-reliability degree information generated for each of thesecond markers 102 in step S404 to the position-reliability degreeinformation table 2051 generated for each of the first markers 300 asillustrated in FIG. 10.

The position-reliability degree information table 2052 generated foreach of the second markers 102, in a manner similar to that of theposition-reliability degree information table 2051 generated for each ofthe first markers 300, includes the ID of the second marker 102, thearrangement position obtained by capture by the camera pair capturingthis second marker 102, the information of the camera pair capturing theimage used in the calculation of the arrangement position, thereliability degree information of the arrangement position, the updatetime and date indicating the time and date at which the arrangementposition is calculated, and the error.

The reliability degree information is set in three stages, that is, A,B, and C in order of decreasing reliability degree. The reliabilitydegree information acquirer 240, for the second marker 102, selects andsets reliability degree information such as the image positionreliability degree information acquired similarly to step S102 of FIG.7, the velocity reliability degree information acquired similarly tostep S103 of the same drawing, the arrangement position reliabilitydegree information acquired similarly to step S104 of the same drawing,the error reliability degree information acquired similarly to step S105of the same drawing, or the like.

Further, for the second marker 102, the reliability degree informationacquirer 240 may be configured to acquire the arrangement position, thereliability degree information, and the error of the second marker 102by acquiring the arrangement position of the first marker 300.

The error is set in three stages as R1, R2, and R3 in order ofincreasing size of the error. The reliability degree informationacquirer 240, for example, sets the error smaller with increasingnearness of the update time and date to the present time and date.

Next, the light-emission position acquirer 236 determines whether thearrangement position is calculated for all of the second markers 102captured in step S401 (step S405). If the arrangement position iscalculated for all of the second markers 102 (YES in step S405), theseries of operations ends. If a second marker 102 exists for which thearrangement position is not calculated (NO in step S405), the operationsof step S402 and beyond are repeated.

By generating and retaining the position-reliability degree informationtable concerning the first marker 300 and the second marker 102 in thismanner, the reliability degree information is acquired for thecalculated arrangement positions of the first marker 300 and the secondmarker 102. Therefore, the arrangement position of highest reliabilitydegree can be calculated for the first marker 300 and the second marker102, and the most appropriate arrangement position can be selected inconsideration of both the reliability degree information and the error.

Further, the identification of arrangement positions can be performedappropriately in cases such as when identification of the arrangementposition is not possible for the first marker 300 and the second marker102 for which only the arrangement position of low reliability degree iscalculated, for the first marker 300 and the second marker 102 for whichthe suitable arrangement position is not calculated in consideration ofboth the reliability degree information and the error, or the like.

Moreover, in the case in which only the position-reliability degreeinformation table 2051 is generated, the arrangement position, thereliability degree information, and the error of the second marker 102can be determined thereafter. That is to say, a case is described belowin which, after generation of only the position-reliability degreeinformation table 2051, and then after removal of the first marker 300from the space 500, the interior of the same space 500 is captured bythe cameras 201 a to 201 d. As illustrated in FIG. 13, after generationand retention of the position-reliability degree information table 2051for the space 500, the first marker 300 is removed, and the secondmarker 102 c is taken to be newly arranged (normal operation state).Then upon capturing images of the space 500 in this state by the cameras201 a to 201 d and then inputting of the captured images to the imageinput unit 204, the image processor 231 detects the second marker 102 cfrom these images. Further, the arrangement position of the secondmarker 102 c is calculated from the matrix and the representations ofthe second marker 102 c in these captured images. Then theposition-reliability degree information table 2051 is referred to, andinformation is read for the first marker (first markers 300 d and 300 ein FIG. 13) 300 captured by the camera pair having a high degree ofreliability and positioned close to the calculated arrangement positionof the second marker 102 c. The error E of the second marker 102 c isdetermined by the below-described method. The error E of the position ofthe second marker 102 c is determined by substitution into the formulaE=(Ef×Xg+Eg+Xf)/(Xf+Xg), in which, as illustrated in FIG. 13, an Xdirection distance between the first marker 300 d and the second marker102 c in the space is represented by Xf, an X direction distance betweenthe first marker 300 e and the second marker 102 c is represented by Xg,an error between the calculated position and the position based onpreviously known information for the first marker 300 d is representedby Ef, and error between the calculated position and the position basedon previously known information for the first marker 300 e isrepresented by Eg.

Further, the present invention is not limited to the description anddrawings of the aforementioned embodiments, and suitable modificationsof the aforementioned embodiments and drawings are possible.

For example, in the aforementioned embodiments, the reliability degreeinformation acquirer 240 calculates the reliability degree information Nconcerning a single second marker 102 under consideration based on theformula N=A×(B1+B2+C3+C2+D), using for each camera pair, the imageposition reliability degree information B1 and B2, the velocityreliability degree information C1 and C2, the arrangement positionreliability degree information D, and the error reliability degreeinformation A that are acquired from the aforementioned processing.

However, the calculation formula is not limited to the above formula,and for example, the image position reliability degree information B1and B2, the velocity reliability degree information C1 and C2, thearrangement position reliability degree information D, and the errorreliability degree information A may be all multiplied together.Alternatively, the reliability degree information acquirer 240 maycalculate the reliability degree information N for the second marker 102by appropriate selection of the image position reliability degreeinformation B1 and B2, the velocity reliability degree information C1and C2, the arrangement position reliability degree information D, andthe error reliability degree information A. For example, a configurationmay be used that does not multiply by the error reliability degreeinformation A when the highest reliability degree information of thesecond marker 102 is less than a threshold. Further, for example, thearrangement position reliability degree information D may be calculatedfor each of the two cameras 201 included in the camera pair. Further, aconfiguration may be adopted that reads and uses the information of thecamera pair having the most recent update time and date.

Moreover, in the aforementioned embodiment, the server 200 selects thecamera pair having the highest reliability degree for the second marker102, and calculates the arrangement position of the second marker 102 onthe basis of the images captured by such a camera pair. However, thecalculation procedure for the arrangement position is not limited tothis configuration.

For example, the server 200 may calculate the arrangement position ofthe second marker 102 on the basis of captured images captured by camerapairs that are all the camera pairs capturing images of the secondmarker 102 using both of the two cameras 201, and may, with increasingreliability degree of the second marker 102 for the camera pair,increase a weighting of the arrangement position of the second marker102 calculated on the basis of capture by these camera pairs. Moreover,the server 200 may be configured to calculate an average value of thearrangement position of the second marker 102 calculated on the basis ofthe images of camera pairs that are highly ranked in reliability degreefor the second marker 102.

Moreover, in the aforementioned embodiments as illustrated in FIG. 6,although the space 500 is partitioned into 9 partitioning regions 501 ato 501 i, the arrangement position reliability degree information istaken to be high if the second marker 102 is present in the partitioningregions 501 a, 501 b, or 501 c, the arrangement position reliabilitydegree information is taken to be intermediate if present in thepartitioning regions 501 d, 501 e, or 501 f, and the arrangementposition reliability degree information is taken to be low if present inthe partitioning regions 501 g, 501 h, or 501 i, the setting of thepartitioning regions 501 and/or the arrangement reliability degreeinformation corresponding to each of the partitioning regions is notlimited to this configuration. The arrangement reliability degreeinformation may differ between each of the partitioning regions 501.

Moreover, although the first marker 300 is stored in association withthe IDs in the storage 205 and in association with the arrangementposition within the space 500, by visible light communication, light maybe emitted that is modulated in accordance with the arrangement positionwithin the space 500.

Moreover, in the aforementioned embodiments, although the reliabilitydegree information within the position-reliability degree informationtable is set in three stages as A, B, and C in order of decreasingreliability degree, this configuration is not limiting, and thereliability degree information may be set to a greater number of stages,or may be set to a numerical value. Moreover, although the reliabilitydegree information is set by appropriate selection of the image positionreliability degree information, the velocity reliability degreeinformation, the arrangement position reliability degree information,the error reliability degree information, or the like, thisconfiguration is not limiting.

Further, although the error within the position-reliability degreeinformation table is set in three stages as R1, R2, and R3 in order ofincreasing size of the error, this configuration is not limiting, andthe error may be set using a greater number of stages, or may be set toa numerical value. Moreover, although the error is set so as to decreasewith increased closeness of the update time and date to the present timeand date, this configuration is not limiting.

For example, the first marker 300 and the second marker 102 are notlimited to LEDs. For example, the marker may include part of an LCD,PDP, EL display, or the like included in a display.

Moreover, the server 200 may be any device to which the cameras areattachable.

Further, a program for execution of the aforementioned embodiments maybe stored and distributed on a flexible disc, compact disc read-onlymemory (CD-ROM), digital versatile disc (DVD), magneto-optical (MO)disc, or the like computer-readable recording medium, and byinstallation of the program, a system may be configured that executesthe aforementioned processing.

Further, the program may be stored on a disc device or the like of acertain server on a communication network such as the Internet and, forexample, may be superimposed on carrier waves and downloaded, or thelike.

Moreover, in the case of realization of the aforementioned functions byexecution allocated to an operating system (OS) or by execution incooperation between the OS and an application, performance of thecontaining and distributing of the aforementioned recording medium, ordownloading or the like, for the non-OS portion alone is permissible.

The foregoing describes some example embodiments for explanatorypurposes. Although the foregoing discussion has presented specificembodiments, persons skilled in the art will recognize that changes maybe made in form and detail without departing from the broader spirit andscope of the invention. Accordingly, the specification and drawings areto be regarded in an illustrative rather than a restrictive sense. Thisdetailed description, therefore, is not to be taken in a limiting sense,and the scope of the invention is defined only by the included claims,along with the full range of equivalents to which such claims areentitled.

What is claimed is:
 1. A position information acquisition device foracquiring three dimensional position information of a positioninformation acquisition target arranged in a space, the positioninformation acquisition device comprising: a processor configured todetect light that is based on identification information includedin-common in captured images that are acquired by capturing images ofthe space using a pair of image capturing devices from a plurality ofshooting directions that are different from each other, the pair ofimage capturing devices being arranged at different positions, acquiretwo-dimensional position information and an imaging direction of each ofthe pair of image capturing devices, based on detection positions of thedetected light in the captured images and two-dimensional positioninformation of the light stored in a storage, acquire three-dimensionalposition information, in the space, of the position informationacquisition target identified by the identification information, fromthe captured images acquired by the capturing by the pair of imagecapturing devices, based on the acquired two-dimensional positioninformation and the acquired imaging directions of the pair of imagecapturing devices, acquire reliability degree information of theacquired three-dimensional position information of the positioninformation acquisition target, based on information relating to anoptical characteristic as information relating to an imaging state ofeach of the pair of image capturing devices during the capturing of thecaptured images, and store the acquired the reliability degreeinformation in the storage.
 2. The position information acquisitiondevice according to claim 1, wherein the information relating to theimaging state is information based on the detection positions of thedetected light in the captured image.
 3. The position informationacquisition device according to claim 1, wherein the informationrelating to the imaging state is information based on a timing ofcapturing the images.
 4. The position information acquisition deviceaccording to claim 1, wherein the information relating to the imagingstate is information relating to movement of the position informationacquisition target in the space.
 5. The position information acquisitiondevice according to claim 4, wherein the processor further acquires theinformation relating to the movement of the position informationacquisition target by comparison of a plurality of the images capturedsuccessively by the image capturing devices.
 6. A position informationacquisition method for acquiring three-dimensional position informationof a position information acquisition target arranged in a space, theposition information acquisition method comprising: detecting light thatis based on identification information included in-common in capturedimages that are acquired by capturing images of the space using a pairof image capturing devices from a plurality of shooting directions thatare different from each other, the pair of image capturing devices beingarranged at different positions; acquiring two-dimensional positioninformation and an imaging direction of each of the pair of imagecapturing devices, based on detection positions of the detected light inthe captured images and two-dimensional position information of thelight stored in a storage, acquiring three-dimensional positioninformation, in the space, of the position information acquisitiontarget identified by the identification information, from the capturedimages acquired by the capturing by the pair of image capturing devices,based on the acquired two-dimensional position information and theacquired imaging directions of the pair of image capturing devices;acquiring reliability degree information of the acquiredthree-dimensional position information of the position informationacquisition target, based on information relating to an opticalcharacteristic as information relating to an imaging state of each ofthe pair of the image capturing devices during the capturing of thecaptured images; and storing the acquired the reliability degreeinformation in the storage.
 7. A non-transitory computer-readablerecording medium recording a program for causing a computer included ina position information acquisition device for acquiringthree-dimensional position information of a position informationacquisition target arranged in a space to function as: detecting lightthat is based on identification information included in-common incaptured images that are acquired by capturing images of the space usinga pair of image capturing devices from a plurality of shootingdirections that are different from each other, the pair of imagecapturing devices being arranged at different positions; acquiringtwo-dimensional position information and an imaging direction of each ofthe pair of image capturing devices, based on detection positions of thedetected light in the captured images and two-dimensional positioninformation of the light stored in a storage; acquiringthree-dimensional position information, in the space, of the positioninformation acquisition target identified by the identificationinformation, from the captured images acquired by the capturing by thepair of image capturing devices, based on the acquired two-dimensionalposition information and the acquired imaging directions of the pair ofimage capturing devices, acquiring reliability degree information of theacquired three-dimensional position information of the positioninformation acquisition target, based on information relating to anoptical characteristic as information relating to an imaging state ofeach of the pair of the image capturing devices during the capturing ofthe captured images, and storing the acquired the reliability degreeinformation in the storage.